There is an ever increasing need for the wireless broadband transmission of audio data for speech or music, from televisions or hi-fi devices, to hearing devices. In particular, transmission should also be possible to a hearing device system with two hearing devices, for the binaural supply.
For the purpose of cordless audio transmission to hearing devices, use is made mainly of FM or infrared devices. These are devices which are worn in place of a hearing device, which are offered as plug-on modules for hearing devices or which are integrated into a hearing device with the need for significant additional space.
For audio transmission, several electromagnetic transmission paths can basically be considered. Thus it is possible, for example, to make use of high-frequency far-field transmission systems and inductive near-field transmission systems. By using a digital, inductive transmission system, it is possible to cover short distances (less than 1 to 2 m) to a hearing device with a saving of space and power. However, for audio transmissions from televisions or hi-fi systems, sensible operation requires a far-field transmission system for larger distances (range approx. 10 m).
From the post-published patent application DE 10 2005 005 603.2, a data transmission facility for wireless transmissions to a hearing device is known, which contains a high-frequency receiving device for receiving a high-frequency, modulated signal from an external transmission unit. A mixing device is used to mix the high-frequency modulated signal with a reference signal of a similarly high frequency, so that a modulated output signal can be generated, the carrier frequency of which is at least one order of magnitude lower, and which is suitable for inductive transmission. Finally, the output signal is transmitted inductively to the hearing device by a transmission device. This conversion method results in a minimal delay time over the entire radio link, because it omits completely any demodulation and decoding plus re-modulation and re-encoding. However, a disadvantage of this transmission is that the entire radio link must be individually established, because the data transmission rate in the high-frequency transmission section and the data transmission rate in the section using inductive transmission must be individually adjusted.